1. Field of the Invention
The present invention relates to an apparatus that performs data transfer by DMA transfer and a method.
2. Description of the Related Art
An image forming apparatus or printing apparatus such as a copying machine or printer includes a plurality of image processing modules, and causes these image processing modules to perform appropriate image processing according to a request for externally input image data. For example, image data is transferred between the image processing modules. Each image processing module sequentially analyzes the data and performs predetermined image processing. Desired image data is thus generated. For example, DMA (Direct Memory Access) transfer is used for data transfer. For example, input image data is temporarily stored in a temporary memory such as a DRAM. After that, the image data to be transferred is sequentially transferred in predetermined units by DMA transfer to an image processing module of a transfer destination.
Japanese Patent Laid-Open No. 2002-140288 discloses a method of switching DMA transfer target data by changing the information of a descriptor in accordance with specifications.
Even when image data is partially commonly used in a plurality of image processes, or image processing is performed in cooperation with a plurality of image processing modules, it is preferable to perform appropriate data transfer according to the contents of image processing and reduce the load on the CPU. In this case, information management is necessary to transfer common image data to the modules. In addition, cooperative operations may be needed among the CPU and the image processing modules to sequentially perform data transfer. However, when such information management or cooperation is achieved by only the descriptor, the load on the CPU increases, and the frequency of access to memories (DRAM and the like) becomes high. This may delay other signal processes and also delay the operation as a whole.